Practical hemodialysis made its debut in the early 1960s with the essentially simultaneous advent of hemodialysis apparatus capable of producing dialysate on line and of hemodialyzers exhibiting an acceptable reliability. Since then, great developments have occurred in hemodialyzers and in hemodialysis apparatus.
Nephrology clinicians have long appreciated the need for hemodialysis to remove not only toxic metabolic solutes from the blood but also excess fluid. Removal of fluid across the semipermeable hemodialysis membrane is termed "ultrafiltration".
The ongoing development of improved hemodialysis membranes has been driven in part by the clinical need to perform ultrafiltration (along with hemodialysis) of a patient in a manner that alleviates patient morbidity as much as possible. With respect to ongoing improvements in hemodialysis membranes, the general trend has been to produce membranes having increased "flux" by which is meant water permeability. Such membranes achieve a more rapid ultrafiltration of water from the blood at a lower transmembrane pressure (TMP). The overarching requirements of safety and well-being for the patient being treated with such membranes have driven the development of hemodialysis apparatus that provide excellent control of ultrafiltration. Such development has been the subject of intensive research by individuals and corporate entities working in the hemodialysis field.
A notable example of a hemodialysis apparatus that provides control of ultrafiltration is disclosed in U.S. Pat. No. 5,247,434 to Peterson et al., which is incorporated herein by reference.
Another trend in hemodialysis has been various approaches to achieving more rapid dialysis (with ultrafiltration) without adversely affecting patient morbidity. According to some approaches, this is achieved by, inter alia, passing dialysate through the hemodialyzer at a higher flow rate than conventionally. In this regard, the conventional dialysate flow rate is 500 mL/min, and some modern dialysis apparatus can achieve a dialysate flow rate of about 1000 mL/min. However, some clinicians perceive a need for dialysate flow rates of 3000-4000 mL/min.
Such increased dialysate flow rates impose a need to achieve greater ultrafiltration rates than conventionally. For example, whereas conventional dialysis apparatus typically achieve an ultrafiltration rate up to about 4000 mL/hr, some clinicians perceive a need for ultrafiltration rates of up to 10 L/hr.
Despite great advances in the art of clinical ultrafiltration, especially ultrafiltration performed during a hemodialysis treatment, conventional apparatus are limited in their ability to satisfy the needs summarized above.